Method of operating electrodes for searchlights



E. A. SPERRY.

METHOD OF OPERATING ELECTRODES .FOR SEARCHLIGHTS.

APPLICATION FILED DEC.22, I915.

' 1,357,827, Patented Nov 2,1920.

2 SHEETS-SHEET I.

. INVENTOR ELMER ASPEPPY ATTOR/VE E. A. SPERRY.

METHOD OF OPERATiNG ELECTRODES FOR SEARCHLIGHTS. APPLICATION FILED DEC. 22. 1915.

1 ,357,827, Patented Nov. 2, 1920.

2 SHEETS-SHEET Z.

INVENTOI? ELMER A. SPEPPY WMM PATENT OFFICE.

ELMER A. SPERRY, 0F BROOKLYN, NEW YORK.

METHOD OF OPERATING ELECTRODES FOR SEARCHLIGHTS.

Application filed December 22,- 1915.

T 0 all whom it may concern Be it known that I, ELMER A. SPERRY, a citizen of the United States, residing at Brooklyn borough, New York city, in the county of Kings and State of New York, have invented certain new and useful Improvements in Methods of Operating Electrodes for Searchlights, of which the following is a specification.

Until the last few years, the standard source of light for searchlights has been the pure carbon arc. While the so called flaming arc lights have been developed for other uses and will give a greater candle power than the pure carbon are, they have been found to be unsuited for projector work as they possess less intrinsic brilliancy than pure carbon. It was thought, as carbon possessed the highest volatilization point of any known substance, that the positive crater of a pure carbon arc possessed the highest attainable intrinsic brilliancy. This hypothesis was borne out by the results attained with flaming arcs, in which the crater brilliancy was invariably lowered by the presence of the flaming materials. It was further observed that the flame possessed a much lower intrinsic brilliancy than a pure carbon crater.

In my U. S. Patent No. 1,227,210, granted May 22, 1917 for method of operating flaming arc lights for projectors, I have disclosed an improved method of operatin flaming arc lights whereby an intrinsic bri liancy far in excess of that obtained by pure carbon or by an ordinary flaming are light is obtained. This invention relates to certain improvements thereof whereby the forming of a deep crater in the positive electrode which is very essential to the success- .ful production of my arc is rendered more certain. In order to understand clearly the advance in the art which this invention represents, I have shown in the drawings a representation of a few of the steps made in the development of the invention.

Referring to the drawings, Figures 1, 2 and 3, illustrate the conditions under which I first observed the superluminescent flame which is the distinguishing feature of my invention, Figs. 1 and 2 showing the different appearances of the flame, and Fig. 3 the appearance of the are after this flame has disappeared. Fig. 4 is an elevation of my are showing the preferred burning conditions, with the two electrodes shown in sec- Specification of Letters Patent.

Patented Nov. 2, 1920.

Serial No. 68,116.

tion. Fig. 5 is a diagram showing a curve plotted with reference to the voltage drop in the different portions of the arc flames. Figs. 6, 7 and 8 illustrate the influence of the total current flowing on the velocity of the negative flame- Figs. 9, 10, and 11 illustrate the influence of current density on the positive flame. Fig. 12 shows the arc operating at a lower amperage but with higher current density than in the preferred form shown in Fig. 4. Fig. 13 is an elevation of one of the positive carbons after burning, showing the slight taper and the graphite ring formed thereon. Fig. 14 is a view of the are under improper burning conditions. Fig. 15 is a front view of my preferred form of arc.

While studying the possibility of employing the white flaming are for projector work, I discovered an entirely new and paradoxical result. Very high grade, homogeneous, white flaming, solid, positive electrodes were employed in which the flame materials were baked in the carbons. The ordinary appearance of a flaming are light is shown in Fig. The carbon consumption is very slow and the positive 1 forms a blunt rounded tip 2. The luminous flame 3 extends across the entire arc length from positive 1 to negative 1. There is furthermore no obversable separation or division between the positive and negative flames. But I observed, while running the are at from 30 to 10 amperes, a sudden and remarkable increase in the brilliancy of a portion 5 of the flame and at the same time the are flame (Fig. 1) appeared to separate into two parts or flames 6 and 7 one of which issued from each electrode. The flames were not entirely distinct, however, as spectrum analysis showed that the flaming arc materials which were contained only in the positive, permeated both flames.

The brilliant portion 5 of the flame appeared to issue from the positive crater. The most baffling discovery was that the intrinsic brilliancy of this portion of the positive flame was much greater than that of pure carbon. Upon a further increase in the current the are assumed more the appearance shown in Fig. 2. Neither are was permanent, however, but would always break down after running a short time and revert to the usual form of flaming arc shown in Fig. 3. I conceived the idea that if this super brilliant flame could be rendered stable and properly controlled or confined, that a source of light would be produced which would be much su erior to the lire-carbon arc.

riefly state a source of light should tuhil the following requirements in order to be suitable for proglector work:

4:. The source should have the maximum intrinsic-brilliancy or candle-power per unit sity, I found that the super-intensive flame til area since the intensity of the beam is dependent directl thereon.

5. As little s adow should be cast on the mirror as possible.

After many experiments I developed a form of flaming arc light-which makes use of the super-intensive flame, mentioned above, to its best advantage. Upon further increase of the amperage and current denbecame more steady and the line of demarcation between the two flames became gradually more sharp. Above 180 to 140 amperes the two flames (Figs. 4:, 12 and 14) became entirely distinct, and the brilliancy of the positive flame became more pronounced. Spectrum analysis of these flames showed that no interchange of elements took place between the flames, so that none of the negative flame reached the positive and vice versa. The two conditions under which the are operated most successfully were high amperage (about 150 amperes) coupled with high current density in the positive electrodes (about 500 amperes per sq. in); Under these conditions an arc of exceptional length (from g in. to 1 in.) was formed.

The appearance of my preferred form of arc is shown roughly in Fig. 4:. Upon considering the requirements for a projector light and comparing them with the qualities of this light, it will be found that this are meets every requirement. A minimum shadow is cast by the negative, since it is far-removed from the positive carbon, the shadow decreasing rapidly with the distance. By far the greater portion of the light is emitted from that portion 8, of the.

positive flame confined within and to the immediate vicinity of a crater 9 which I cause to be formed by a method hereinafter described. This flame is allowed to escape, if at all, only at the top of the crater. This flame vapor is produced much more rapidly than the vapor from the negative carbon.

It seems to consist of a homogeneous mass cate that the entire brilliancy or emissivity issues from the flame, and that but a small portion of the total light issues from the carbon itself. This, of course, is in sharp contrast to the present type of sea-rchlights in which practically the entire light issues from the surface or tip of the positive electrode.

The negative flame 9, it will be noted, seems to comprise several zones or parts. The inner zone (a) which is hereinafter referred to as the tongue, is a very high velocity stream at the very center of the negative flame. It is the most luminous part of the flame and appears of a yellowish color. Zone (6) surrounds this tongue and is also of higher velocity than the outer portions of the flame but has very little luminosity. Zone (0) is a very thin sheath surrounding this nonluminous zone, is of a purple color, and seems to be only a bright inner lining for zone The latter zone comprises the main bod of the negative flame and is the color an brilliancy of the ordinary arc flame between carbon electrodes. It should be noted that it is this zone which is made use of as an impinging force against the positive flame to properly control it as here inafter explained. Zone (6) is the outer mantle of a ruddy color which is present in all arcs and is probably due mainly to the combustion of the outer portions with the air. Although the negative flame consists of the above mentioned zones, it always behaves as a unit so that while it is possible to control the direction of the entire flame one part can not be controlled irrespective of the other parts.

The positive electrode 1', itself prefer ably consists of an outer shell 13 of pure carbon and an inner core 14 which contains especially prepared but well known white flaming arc materials. These materials may comprise cerium or other rare earth fluorids or the like, which should be uniformly baked in the carbon. rials used, however, not only serve to increase the luminosity of the flame, but are made so as to aid in the formation of the crater 9 mentioned above. The formation of this crater is one of the most important portions of my invention, and positive means are therefore taken to insure its be- The mateadmixture of materials in the core in the formation of the dee crater may be explained as follows: he anode drop from the highly refractory, though pure, carbon shell to the arc is much higher than the corresponding drop from the special impregnated core to the arc. that when the arc is struck there is a strong tendency of the core to burn back or recede to a depth sufficient to equalize the voltages in the two cases. That is, the anode drop from the core plus the drop through the flame within the crater approaches in equality, the anode drop from the pure carbon shell. But, even with carbons of the above characteristics, a crater will not form under the conditions present in the ordinary white flaming arc. This is caused by the rapid burning away of the perimeter of the carbon shell which is in all probability due primarily to contact with the air or with the negative flame. This difliculty is automatically overcome in my lamp by striking a balance between the refractory qualities of the shell and the current density employed to burn the positive carbon away with just suflicient rapidity so that only a predetermined, but important spindling takes place. This spindling of the carbon is so regulated under these conditions, that it will not be suflicient to interfere with the crater, on the one hand, while on the other it possesses the important advantage that a smaller light source is thereby produced.

In order to illustrate further this action in the formation of the crater, I will point out at this point, the electrical characteristics that I observe with this form of are light. By exploring with slender carbon rods within the two arc flames, and noting the voltage drop that took place in the different positions, I was enabled to plot the curve shownin Fig.5.

The curve is laid out with units of arc length for abscissae and volts for ordinates. From this it will be noted that the cathode drop is in the neighborhoodof 9 volts and the drop through the negative flame approximately 15 volts, and that the total drop of the positive flame and anode is in the neighborhood of 47 volts. The cathode drop, it will be noted, is the same as in the pure carbon arc, while theanode and positive flame drops could not be measured separately, as the exploring rods could not be inserted within the crater without extinguishing or distorting the are. I did not deem it necessary to determine directly It therefore follows 7 this value, as the anode drop for ordinary white flaming arcs is known and results obtained indicate that the anode drop of the. special core remains about the same as for the ordinary flaming arc, i. 6., about 13 volts, this being very much less than the 36 or 37 volt drop for pure carbon. It will thus be seen that'one of the important results of the special impregnated core is to secure this greatl reduced anode drop, for reasons which Wil presently appear.

Let us now consider the most striking feature of the curve, viz., the tremendous drop in voltage that takes place in the short positive flame which is largely, if not wholly, confined within the crater. This shows that an enormous amount of energy is expended within and adjacent the crater and, when the current density is also taken into account, the energy density proves to be 3.6 times as high as the energy density of the pure carbon positive crater. A rough calculation of the energy consumed in this flame will show that something like five to ten kilowatts are consumed within the short length of the positive flame which as is shown in the diagram seldom exceeds 15 mm. This tremendous concentration of energy consumption doubtless explains easily the super-luminosity of the positive flame. The presence of the aforesaid special mixture of flaming arc materials not only has the effect of reducing the anode drop as stated and of adding luminosity to the flame, but also performs an additional important function of at least increasing in effect the specific resistance of the positive flame under the conditions stated as is evidencedby the large voltage drop therein. So that although the difference between the anode drops of pure carbon and the impregnated core is, roughly speaking, 22 to 27 volts, the flame does not have to be a long one nor does the crater have to be dug very deep to produce a suflicient column of luminescent vapor to cause this additional 22 to 27 volt drop between the bottom and mouth of the crater, due as stated, to the specific resistance of this vapor column being very high. It is not essential to this discussion that we should understand the true scientific nature of this resistance. Whether it is due to electro-chemical action or whether it is physical or simply resistance is as yet problematical.

Proper burning conditions are also very important. Thus, as stated above, the positive flame should not be allowed to escape from the crater, but should be closely confined. If allowed to escape at all it should be directed from the crater in a certain definite direction preferably upwardly at the top of the crater. This will confine the burning portion of the shell to a comparatively small portion of the rim or lip. The proper control of the positive flame is best effected bymeans of the negative flame 9. When employing high currehts it is always found that the negative flame possesses considerable velocity. This phenomenon seems to.

nearer the positive electrode The currents used in these tests were 7, 15 and 25 amperes in Figs. 6, 7 and 8 respectively.

In order to cause the negative flame to perform practically and yield the best results I have found that it should be given a positive directive force since otherwise the direction of the flame is apt to vary and the steadiness of the are be adversely effected. To illustrate the importance of this feature, especially for a large and therefore an'unobstructed arc, I may state that I found this arc to be inherently unsteady even to an extent which will cause it to lose the positive and negative flames 9 the greater portion of its brilliancy unless a Well defined steadying force is given to the negative flame or blast which will prevent any deflecting pressure such as upward air currents from changing or altering this direction.

For instance, if a solid negative carbon 3' is employed, the requisite arc length maintained and no other extraneous means are provided for directing the negative flame,

and 8 tend to ride up on each other as shown in Fig. 14, making a high arch 10, and the voltage across the arc increases to such an extent that the arc is very unsteady and most easily extinguished. Also it is to be noted that the negative flame does not issue steadily from the tip, but shows a tendency to issue from the top as shown at 25.

T have tried various directive influences upon the negative arc flame. The preferred form may be stated as follows: I have discovered that a sma l core 10, preferably more rapidly burning than the shell and containing arc sustaining materials, can be made to give just the desired directive influence to the negative flame to prevent the above mentioned trouble when maintaining the proper/arc length. Such a core also confines the flame to the tip 11 of the negative. electrode, which burns almost invariably concave or into a small crater 12. In 1 addition to the core, I prefer to provide a re reat copper coating 32, on the negative to increase its conducting capacity. In order to use this directive negative blast so that it may confine the ositive flame to the best advantage, if fin it necessary because a definite impinging contact between the two flames across the crater mouth in such a manner as to utilize the broad zone at of the negative flame so that it entirely covers the mouth of the positive crater and thereby serves to impinge the whole body of positive va or, not allowing it to issue at either side. lit 1s also important that a steady and somewhat upwardly inclined current be created at the contact of the two flames.

-This sort of impingement may be such that it still al ows a steady, but not too free, escape of some of the spent positive luminous vapor in a constant direction and thus prevents flarin and flickering of the are which results w en the flame from the positive crater is allowed to escape in any undetermined direction, as it is necessary that it remain under perfect control by the negative flame. This sidewise impingement of the negative with the positive flame may be best secured by positioning the negative electrode at an angle to the positive electrode as shown in Fig. t, but I make no claim to this angular positioning, per so, since all sorts of angles have heretofore been used and proposed in this art.

I am aware that attempts have been made to increase the steadiness of the are by using negative electrodes witha core of more refractory material than the shell so that the negative will burn to a slender point. It wil be noticed that I prefer to employ carbons having just the reverse burning characteristics, inasmuch as the core is more rapidly burning than the shell, invariably producing a definite concavity or crater 12 at the tip of the negative, which persistently aids in imparting a definite directive force to the negative flame. Another important eflect of the negative core is to aid in maintaining a long arc, the advantages of which were above pointed out.

The velocity and pressure/of the positive flame is also of great importance, since this flame should on the one hand not be strong enough to push into or through the negative flame and on the other hand it should be strong enough to push its way out at least to the mouth of the crater so as to secure the important function of light saturation above pointed out with regard to this flame so that it may obscure to the proper extent the lower light intensity of the crater surface-l ing behind it. After many experiments, l determined that the velocity of the positive made to even push its way through the high velocity stream of the negative flame. It

therefore appears that I have discovered a simple and dependable method of controlling the relative velocity of the two flames, and hence the depth of the positive, namely by varying the total current flowing and the current density in the positive electrode.

Another portion of my invention that is dependent upon these factors is the appear ance of the superluminescent positive flame, upon which the success of this invention is dependent. As above pointed out this phe nomenon which I have termed the high intensity effect seems to be dependent to some extent on the total current flowing. But the current density at the tip of the positive electrode also plays an important part. Thus in the preferred form shown in Fig. 4, a current of 150 amperes is being used with a positive electrode of 16 mm. diameter. If the same electrode is retained and the current reduced, the high intensity effect will almost entirely disappear at about 100 amperes, but if the size of the electrode 1 is reduced, the high intensity effect will appear in permanent form at much lower currents. Fig. 12 shows the appearance of the arc employing 90 amperes with a ositive electrode 30 of 11 mm. diameter. Fhe arc will also possess a similar appearance with 80 amperes and an electrode of 8.5 mm. It should be noted however, that in order to retain this eflect as the current is decreased, that the current density must be increased, so

that a point is soon reached where the resistance of the positive electrode becomes a serious drawback. It also appears probable that the high intensity effect cannot be made to appear when the total current flowing falls below a certain minimum, no matter what current density is employed.

The above tests were made with carbons which were shielded from oxidation closely behind the tip by a highly refractory sleeve. Similar results may be obtained however, without a shield, if larger carbons are used to maintain the cross section at the crater of the same diameter, since spindling will take place for a considerable distance back of the tip, if the carbon is exposed to the air.

, In order to maintain the depth and symmetry of the crater I also find it desirable burning away of the upper lip. But, furthermore, when the arc is operating as shown in Figs. 4 and 12, the emitted or exhausted vapor from the arc and a portion of the negative flame licks the outer rim of the positive crater as it turns and deposits on the outside of this rim a continuous graphite ring 23 which performs the extremely useful function of. protecting the positive carbon from excessive tapering at the outer edge of the crater or electrode tip, which, being the hottest portion of the positive electrode, exposed to the air, is the part for which protection is most necessary. Under some operating conditions, this graphite ring is found to build out beyond the shell as shown in Fig. 12 at 31 where it adds very materially in the formation and maintenance of the crater.

Having described my invention, what I claim and desire to secure by Letters Patent 1s:

1. The method of securing a deep symmetrical crater of a positive flaming arc electrode for obtaining the high intensity effect which consists in employing a positive flaming arc electrode having a carbonaceous shell and a core, the latter containing a salt of cerium or other rare earth uniformly baked therein and having a lower anode drop than the shell, impressing a high current density on said electrode and rotating the same whereby the positive flame is substantially restricted to the crater so produced.

2. The method of securing a deep symmetrical crater as claimed in claim 1 in which the carbonaceous negative electrode employed has a carbonaceous core containing are supporting material.

In testimony whereof I have affixed my signature in the presence of two witnesses.

ELMER A. SPERRY.

Witnesses:

WILBERT G. SLoA'r, EDWARD H. KEISER. 

